Biochemically, the cerebellum is characterized by a large concentration of cGMP, cAMP, and cGMP-dependent protein kinase. Drug-induced changes in GABA receptor function can be easily monitored by measuring changes in these biochemical parameters. It is suggested that diazepam and muscimol (a modulator and a direct GABA receptor agonist, respectively), modulate cerebellar function by altering the cGMP system. Diphenylhydantoin has its own receptor on cerebellar structures and this receptor is modulated by benzodiazepines.